The present invention relates in general to adaptive front-lighting systems for vehicles, and, more specifically, to a fuzzy logic control system for sequentially illuminating supplemental LED light sources in response to vehicle speed and turning radius.
Exterior lighting systems known as Adaptive Front-lighting Systems (AFS) have been introduced on motor vehicles to increase traffic safety at night by directing light forward of the vehicle according to speed, direction, and the presence of other vehicles. An AFS system may include an array of light-emitting diodes (LEDs) with optics to generate a beneficial beam pattern, an electronic power driving system, and an onboard micro-controller to activate various ones of the LEDs in the array as needed. In a preferred embodiment, the LED array provides light in a beam pattern that is supplemental to a main light source such as an incandescent or high-intensity discharge (HID) source that provides a constant (i.e., low beam) illumination.
In order to achieve optimum light distribution without distraction to the driver, it is desirable to smoothly increase or decrease the supplemental lighting as the conditions requiring the supplemental lighting change. The LEDs are typically driven in a sequential manner with a first LED being activated first which has a supplemental beam pattern closest to the main beam. As more supplemental lighting is needed, additional LEDs are activated which provide a beam pattern progressively farther from the main beam. Furthermore, each LED is ramped in brightness between fully off and fully on. Thus, the electronic controller generates a variable driving signal in response to instantaneous conditions so that as more supplemental illumination is needed, it activates the first LED with an increasing brightness until it is fully illuminated and then activates the second with increasing brightness, and so on.
Typical vehicle conditions for controlling the AFS include vehicle speed and turning radius because a wider illumination pattern is desired while turning, but the degree of increase also depends on the speed at which the turn is taken. It has been suggested that a controller for such an AFS may be based on fuzzy logic (see Lukacs et al, Impact of Adopting Fuzzy Logic to Control an LED AFS (adaptive front-lighting system), SAE Technical Paper Series 2007-01-2784, 2007). However, what has been lacking are methods for the derivation of actual rules for a fuzzy logic controller that can be efficiently obtained while providing optimized performance according to a type of vehicle (e.g., passenger car, light truck, or heavy truck) and driving environments of different geographic locations where a vehicle is used (e.g., various countries with right-hand drive versus left-hand drive or with different standards of road building or types of city versus rural infrastructures).